1. Field of the Invention
The present invention pertains to navigational systems for determining the location of a moving vehicle such as a boat, truck, automobile or airplane. More particularly, the present invention relates to an automatic system for determining the location of a vehicle in relation to two or more known commercial AM or FM radio transmission antenna or any other radio signal source of known location and frequency.
2. Description of the Prior Art
Various types of equipment and systems for assisting in navigation and determining the location of a vehicle such as a boat, truck, automobile or airplane are known to the art. In the area of maritime navigation, the best known and most extensively used commercial system is known as Loran-C. Loran-C is an improved version of Loran-A which was developed during World War II. A Loran-C receiver measures the difference in time of arrival of two different specially transmitted radio signals, one from a master Loran-C transmitting station, the other from a secondary Loran-C transmitting station. Because the Loran-C signals travel at a known speed (the speed of light), a time-difference reading allows the navigator to plot a position as a line of position on a chart. To get an accurate fix of position, yet another reading must be taken from a third Loran-C station to find the intersection of the two time differential lines. While Loran-C is a significant improvement over the Loran-A system, which had numerous deficiencies, Loran-C still is not extremely accurate and has limited utility close to shore or close to the source of the signals. Further, Loran-C is dependent upon special transmitting stations and cannot be used except in the proximity of such stations.
Similarly, aircraft navigational systems are dependent upon special beacon radio stations that transmit at special frequencies. One such system is illustrated in U.S. Pat. No. 2,569,328-Omberg. Neither Loran-C or the aviation system is adaptable for multiple use by different types of vehicles. Loran-C is limited to marine use and the aviation systems are limited to use in airplane navigation.
Also, with the advance of space technology, satellite navigation systems such as that disclosed in U.S. Pat. No. 3,304,551-Kikuo Oki et al. are being used more frequently. However, such systems are extremely expensive to set up and presently are used to determine locations of very large ships at sea periodically as the navigational satellite passes overhead.
For smaller marine vessels, for example, manual techniques have been utilized for years to find the position of a vessel. Directional sensitive antenna are well known and have been used for years to determine the null angle to known radio stations. With at least two null angles and a chart having a location of the radio antenna plotted, the position of the vessel can be roughly determined by triangulation on a chart. However, such manual techniques are time consuming, inaccurate and usually difficult if not impossible to perform when the vessel is rolling or tossing in heavy waves. Unfortunately, it is during such times of possible distress that accurate positional information is most important for the safety of the vessel and its passengers.
Further, there is no known system for quickly and accurately determining the location of a truck or automobile. While such information is of limited value to most motorists, a system that can monitor and record vehicle travel would be very beneficial to many businesses that depend upon economical truck delivery. A system that could accurately determine and record the periodic location of delivery trucks would be useful in eliminating excess costs resulting from poor performance of lazy drivers.
Thus, it would be a substantial advance in the art to have a small compact inexpensive system which may be utilized in small vehicles such as pleasure boats, motor vehicles, or private airplanes which could automatically and very accurately determine the exact location in respect to two or more commercial AM radio transmitting antenna. Such commercial radio transmitting antenna may be found throughout the world. Thus, no special transmission equipment or antenna need be installed and the system can be used anywhere that there are commercial radio stations.